The present invention relates to a steam generator utilized for a liquid-metal coolant reactor and more particularly, to a steam generator in which an electromagnetic pump is incorporated.
In a fast breeder reactor utilizing a liquid-metal coolant, a primary coolant as a reactor coolant is exposed high levels of to radioactivity, so that it is necessary to isolate a primary cooling system from a steam generation system, and it is also necessary to carry out a heat exchange operation between the liquid metal and water during the steam generating process for supplying the steam to a turbine generator. However, in a fast breeder reactor utilizing a liquid-metal coolant, since an extremely large amount of heat is generally generated due to a chemical reaction based on the heat exchanging operation between the liquid metal and the water, it is necessary to disperse the heat generated. For this reason, a secondary cooling system is generally located between the primary cooling system and the steam generation system.
A typical example of a cooling system of the liquid-metal coolant reactor of the conventional type described is shown in FIG. 8. Referring to FIG. 8, in a reactor vessel 1, disposed in a roof slab 8, are arranged a reactor core 2 and a primary cooling system comprising a primary main circulation pump 3 for circulating a liquid-metal coolant in the reactor vessel 1 for cooling the core 2, and an intermediate heat exchanger 4 for carrying out the heat exchanging operation between the primary coolant and the secondary coolant.
On the other hand, a secondary cooling system comprises, as shown in FIG. 8, the intermediate heat exchanger 4, a steam generator 5 for generating steam to be supplied to a turbine generator, an electromagnetic pump 6 arranged inside the steam generator 5 for circulating the secondary coolant, and pipings 7 for connecting the equipment described above.
The steam generator 5 is disposed outside the roof slab 8 which is surrounded by a wall structure of the reactor.
The electromagnetic pump 6 is inserted into an upper portion of a liquid-metal outlet rising pipe 11 for sucking the liquid-metal from the lower portion of the rising pipe 11 and for feeding the same towards the intermediate heat exchanger 4. The electromagnetic pump 6 is generally provided with a stator coil (electromagnetic coil) wound around the outer periphery of an inner iron core in a spiral fashion, and an electric current is conducted to the stator coil from an external power source to thereby generate a magnetic field to cause the circulation of the liquid metal.
During the conduction of the electric current and the operation of the electromagnetic pump 6, heat is generated from the stator coil. Accordingly, it is desired to effectively remove and disperse this heat during the operation thereof. For this purpose, various trials have been carried out for effectively absorbing the heat generated from the stator coil and recovering the same into the metal-liquid to suppress the energy loss during the operation of the reactor to a minimum. FIG. 9 shows one example of an electromagnetic pump proposed for the purpose of achieving the effect described above and disclosed in Japanese Utility Model Laid-open Publication No. 116701/1988.
An electromagnetic pump 20 shown in FIG. 9 comprises an inner iron core 22 provided with an inner through hole 21 and an outer iron core 23 arranged concentrically with space around the outer periphery of the inner iron core 22. The space between the outer periphery of the inner iron core 22 and the inner periphery of the outer iron core 23 is formed as an annular passage 24 through which the liquid metal passes. A first stator coil (electromagnetic coil) 25 is embedded in an annular fashion in the outer peripheral surface of the inner iron core 22, and the outer surface of the first stator coil 25 is completely covered with a sealing member 26. Both of the vertical ends 26a of the sealing member 26 extend beyond the outer end portions of the inner iron core 22 and are connected with each other to be closed and thus define inner spaces 27 at both the ends of the iron core 22. These inner spaces 27 and the through hole 21 are filled with inert gas.
A second stator coil (electromagnetic coil) 28 is embedded in an annular fashion in the inner peripheral surface of the outer iron core 23 and the outer surface of the second stator coil 28 is covered with a sealing member 29. The outer periphery of the outer iron core 23 is surrounded by an annular member 31 having its outer periphery supported by an electromagnetic pump supporting cylinder 29a.
A plurality of bypass passages 32 are formed in the annular member 31 along the axial direction of the outer peripheral surface of the outer iron core 23 and the upper ends and the lower ends of the bypass passages 32 are provided with bypass passage inlets 33 and the bypass passage outlets 34, respectively.
The electromagnetic pump 20 of the structure described above is secured to a flange member 35 which is secured to a flanged portion of the steam generator 5 used to install the electromagnetic pump 20 in the steam generator 5.
The electromagnetic pump 20 operates to draw the liquid metal from a suction port 36 by the magnetic force caused by the first and second stator coils 25 and 28, and the drawn liquid metal flows upwardly in the annular passage 24 and is discharged through a discharge port 37. During this operation, the pressure at the inlet portion 33 of the bypass passage becomes larger than that at the outlet portion 34 of the bypass passage, so that a part of the liquid metal passes the bypass passages 32 and circulates around the outer iron core 23. The first stator coil 25 then generates heat, which is effectively recovered by the liquid metal to thereby suppress the temperature rise due to the heat generated by the first stator coil 25. The recovery of the generated heat by means of the circulating liquid metal possibly minimizes the energy loss in whole the steam generator.
However, with the conventional steam generator of the character described above, the axial through hole 21 of the inner iron core 22 constituting the electromagnetic pump 20 and the spaces 27 defined by the sealing member 26a are closed and the spaces are filled with the inert gas, so that the first stator coil 25 embedded in the inner iron core 22 is cooled by only the liquid metal passing the circular passage 24. For this reason, the cooling effect for the first stator coil 25 of the inner iron core 22 decreases and the temperature rise of the inner iron core 22 is increased, whereby the characteristics of the electromagnetic pump 20 cannot be effectively utilized.